@Quick:

wpoll paid attention in class and did a fine job of explaining.

You are correct in saying the OP "should" be doing as described. The fact it does not indicates a failure and the text 6 will weed out that failure.

When operating normally, both fuel sensors will start to move once about 10L has been consumed. (Before that they are both "pinned" against the top of the tank. (for all those wondering why it takes so long for any car to have the fuel gauge drop from full. That is why).

As fuel is spent from the X5, the right side being smaller will drop to near zero while the left side will drop to about 30L. At this point, the left and right sides will become separate.

Since there is only one fuel pump and that is on the right side, the siphon jet delivers a constant stream of fuel from the left side to the 5L "surge tank" or well on the right side where the electric fuel pump lives.

When operating normally, the siphon delivers far more fuel than the engine can consume so the right side is filled to overflowing and spills right back to the left side. If the siphon jet is not working properly it's usually that o-ring defect or maybe 10% chance the electric fuel pump is weak. (makes enough psi for the engine but not enough left over to operate the siphon).

Everybody with an X5 should run test six and drive down to single digits miles to empty to confirm the right side of the tank will hold steady to the bitter end.

If the right value gets to zero before the left, there is a failure that needs to be addressed. 90% chance siphon jet o-ring, 8% chance soft fail fuel pump, 2% something else like FPR or siphon pressure release valve or plugged foot.

If tracked many dozen threads on the topic, I only saw maybe two that were a soft fail electric pump the rest all siphon jet, sadly most people replaced the whole left fuel assembly rather than just the 50¢ o-ring.


Sent from my iPhone using Tapatalk Pro

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)